This invention relates to a slider having a plurality of resilient contact fingers slidably engaging an electric conductor. The slider is used in particular for variable electric resistors which find application, for example, in measuring or regulating instruments. The invention also relates to a method of manufacturing such a slider and further, to a resistor incorporating the slider.
It is known that in variable resistors, particularly of the relatively high-ohmic type, the contact resistance between the slider and the conductor (resistor track) varies along the path of regulation. This phenomenon adversely affects the accuracy of setting as well as the fidelity of current transfer and further causes operational noises.
Assuming that a carbon or cermet resistor track consists of infinitely small particles in perfectly homogeneous distribution and further assuming that the slider has a perfectly spherical surface, in first approximation a noise-free operation and a constant contact resistance would be achieved along the path of regulation. In practice, however, these requirements cannot be accomplished with resistor tracks formed either of wire coil resistors or granules distributed in a carrier substrate. For this reason, in most known structures, linearly or quasi-spherically shaped contact elements of increased contact surface are used with the application of correspondingly high contact pressures.
For maintaining the contact resistance at an as low and as constant a value as possible, the contact pressure has to be maintained constant at an accurate predetermined value. This contact pressure -- which is necessarily high -- causes an undesired and often premature wear of the path of contact of the resistor track.
It is known to use in sliders of the above type a plurality of resilient leaf spring fingers arranged in a fan-like manner. Sliders are further known which comprise a wire helix contacting the conductor track at several points to obtain a plural, although linear, contact arrangement.
The plate cross section oriented perpendicularly to the direction of slider motion ensures a favorable moment of inertia of the contact fingers. The linear contact -- which is more likely a surface contact -- conventionally resulting from such an arrangement is, however, disadvantageous. According to another known solution, a resiliently arranged helix of curved axis is used as a multiple contact. This arrangement is advantageous in that the individual contacts (elemental contacts) are in engagement with the resistor track along a cylindrical surface. Thus, in principle, a linear contacting is ensured. On the other hand, however, this arrangement has the disadvantage that the moment of inertia perpendicularly to the direction of slider motion is small. This is so because the moment of inertia is determined by the cross section of the helix wire and the exact reproduction of the once set angle value is affected precisely by the elasticity of the helix. Thus, in this case no stringent requirements can be established regarding reproducibility.